D. PHAEODARIA (CANNOPYLAEA, Haeck.; TRIPYLAEA, Hertw.).—Central capsule spheroidal, of two layers, in its outer layer an operculum, with radiate ribs and a single aperture, beyond which protrudes the outer layer; osculum basal, a dependent tube (proboscis); accessory oscula, when present, simpler, usually two placed symmetrically about the apical pole; skeleton siliceous, with a combination of organic matter, often of hollow spicules; nucleus sphaeroidal, eccentric; extracapsular protoplasm containing an accumulation of dusky pigment granules ("phaeodium"). {77}[Illustration: FIG. 23.—_Actinomma asteracanthion._ A, the shell with portions of the two outer spheres broken away; B, section showing the relations of the skeleton to the animal, _cent.caps_, Central capsule; _ex.caps.pr_, extra-capsular protoplasm: _nu_, nucleus; _sk._1, outer, _sk._2, middle, _sk._3, inner sphere of skeleton. (From Parker and Haswell, after Haeckel and Hertwig.)] A. SPUMELLARIA. Sublegion (1). COLLODARIA.[86]—Skeleton absent or of detached spicules; colonial or simple. Order i. COLLOIDEA.—Skeleton absent. (Families 1, 2.) _Thalassicolla_ Huxl.; _Thalassophysa_ Haeck.; _Collozoum_ Haeck.; _Collosphaera_ J. Müll.; _Actissa_ Haeck. Order ii. BELOIDEA.—Skeleton spicular. (Families 3, 4.) Sublegion (2). SPHAERELLARIA.—Skeleton continuous, latticed or spongy, reticulate. Order iii. SPHAEROIDEA.—Skeleton of one or several concentric spherical shells; sometimes colonial. (Families 5-10.) _Haliomma_ Ehrb.; _Actinomma_ Haeck. (Fig. 23). Order iv. PRUNOIDEA.—Skeleton a prolate sphaeroid or cylinder, sometimes constricted towards the middle, single or concentric. (Families 11-17.) Order v. DISCOIDEA.—Shell flattened, of circular plan, simple or concentric, rarely spiral. (Families 18-23.) Order vi. LARCOIDEA.—Shell ellipsoidal, with all three axes unequal or irregular, sometimes becoming spiral. (Families 24-32.)[87] {78}[Illustration: FIG. 24.—_Xiphacantha_ (Acantharia). From the surface. The skeleton only, × 100, (From Wyville Thomson.)] B. ACANTHARIA. Order vii. ACTINELIDA.—Radial spines numerous, more than 20, usually grouped irregularly. (Families 33-35.) _Xiphacantha_ Haeck. Order viii. ACANTHONIDA.—Radial spines equal. (Families 36-38.) Order ix. SPHAEROPHRACTA.—Radial spines 20, with a latticed spherical shell, independent of, or formed from the reticulations of the spines. (Families 39-41.) _Dorataspis_ Haeck. (Fig. 25, A). Order x. PRUNOPHRACTA.—Radial spines 20, unequal; latticed shell, ellipsoidal, lenticular, or doubly conical. (Families 42-44.) C. NASSELLARIA. Order xi. NASSOIDEA.—Skeleton absent. (Family 45.) Order xii. PLECTOIDEA.—Skeleton of a single branching spicule, the branches sometimes reticulate, but never forming a latticed shell or a sagittal ring. (Families 46-47.)